Positive rotation cleanout apparatus and method

ABSTRACT

Apparatus for retrieving drill pipe, drilling tools, or other equipment stuck in a well bore has a selectively insertable, positively rotating drill bit which can clean out the box end of a collar or tool to enable a fishing string to engage the stuck object, and can clean out the bore of a well pipe to enable lowering therethrough of an explosive charge as an aid to retrieving the stuck object. A method for retrieving drill pipe, drilling tools, or other equipment stuck in a well bore is also provided.

United States Patent [191 Carothers [451 May 7,1974

[ POSITIVE ROTATION CLEANOUT APPARATUS AND METHOD [75] Inventor: William F. Carothers, Houston, Tex.

[73] Assignee: Wilson Industries, Inc., Houston,

Tex.

[22] Filed: Oct. 13, 1971 [21] Appl. No.: 188,876

[52] US. Cl 166/301, 166/99, 175/257 [51] Int. Cl E2lb 31/00, E2lb 41/00 [58] Field of Search 166/99, 178, 192, 202,

[56] References Cited UNITED STATES PATENTS 3/1960 Alexander 166/301 5/1963 Clark,.1r. 166/99 1/1966 Lagerstrom 175/257 3,000,440 9/1961 Malcomh 175/321 2,935,130 5/1960 Moore 2,305,261 12/1942 Kinley 166/299 Primary Examiner-Henry C. Sutherland Assistant E.raminer.lack E. Ebel Attorney, Agent. or Firm-Arnold, White & Durkee [57] ABSTRACT 18 Claims, 5 Drawing Figures PATENTEDm 1 m4 SHEET 1 U? 2 FIGIB FIG. 1A

PATENTEDHAY 7 I974 SHEET 3 BF 2 FIG. 3

POSITIVE ROTATION CLEANOUT APPARATUS AND METHOD BACKGROUND OF THE INVENTION The present invention relates to apparatus and methods for retrieving well-drilling equipment stuck in a well bore, and more particularly, to apparatus and methods for removing material plugging an object stuck in a well bore.

[n the drilling of wells it is a common occurrence for drill pipe, drilling tools, or other equipment to become stuck in the well bore. Such stuck objects are commonly called fish," and the operations undertaken in attempting to recover such objects are called fishing." The cause of a fish becoming stuck is usually a collapse of the well bore around the outside of the fish. Often on removing the drill string above the stuck pipe, rocks or other debris fall into and plug the bore of the pipe. Drill bits may also become stuck as they are pulled from a well when the well bore contains a key seat, which is an offset, recessed portion of the bore having an effective diameter less than that of the well bore proper.

The general practice in attempting to recover a fish is first to remove all the pipe above that portion which is stuck. If the well bore has collapsed around the outside of the fish, a wash pipe is lowered into the bore to wash over and free the fish from contact with the formation. As the upper end of the fish is usually the box of a box-and-pin connection, the retrieving assembly is usually a mating pin. If the upper bore, or box, of the fish is plugged, the fishing string is often unable to engage the fish. Steps commonly undertaken at this point include lowering a wash pipe within the fishing string and circulating fluid downwardly through the fishing string and wash pipe in an effort to wash the plugging material from the bore of the fish. If the washing operation is not successful, for example, because the plugging material is rock, the next step in the fishing operation is usually an attempt to break up the rock by pounding it with the fishing string. Tools which may be used with a fishing string for such pounding operations are well known to those practicing the art. These efforts are not uniformly successful, however, and are further undesirable because they may result in damage to the fish or to the fishing string. ln particular, damage to the threads within the box end of the fish may make subsequent fishing operations much more difficult and expensive.

When the material plugging the upper bore of the fish has been successfully removed, the fishing string may engage the fish. Upward pulling and jarring forces are then applied in an attempt to remove all of the stuck equipment. When the upward pulling and jarring are unsuccessful because, for example, the well bore has collapsed around lower sections of the fish, that portion of the fish which is no longer stuck is removed and retrieving operations are undertaken on the remainder. Removal of the free portion of the fish is often accomplished by methods involving the lowering of an explosive charge on a wire line to a point inside the fish and opposite the joint to be disengaged, and firing the charge to release the joint. The release of a section of stuck pipe by this method is well known to those ordinarily skilled in the art of fishing.

When it is desired to lower an explosive charge through the fish to aid in disengaging the first joint of the fish above the stuck portion. i.e., where the washover ended, the presence of material plugging the bore of the fish below its uppermost box joint creates an additional problem. Such material must be removed in order to enable placement of the explosive charge in the proper location for disengaging the joint. Washing, spudding, and hydrostatic bailing have commonly been used to remove such debris. but these operations are frequently unsuccessful when the plugging material is rock. If the plugging material cannot be removed, the proper positioning of the explosive charge is not possible. The only alternatives are to make outside mechanical cuts in an effort to remove the fish or to abandon the stuck equipment in the well, both of which are extremely costly.

SUMMARY OF THE INVENTION The present invention relates generally to a new and improved apparatus and method for use in retrieving drill pipe, drilling tools, or other equipment stuck in a well bore, and more particularly to apparatus and methods for removing rock and other debris from the bore of drill pipe, drilling tools, or other equipment stuck in a well bore by positive rotational drilling of the rock or other debris from the bore of the stuck equipment.

The apparatus of this invention comprises a sub which is adapted to be located near the lower end of a fishing string and which includes means for forming a positive rotational driving engagement with drill means passing through the sub.

It is, therefore, one object of this invention to provide drill means adapted to be selectively lowered in a fishing string, engaging a positive rotational driving means in the fishing string to rotationally drill out debris plugging an object stuck in a well bore.

his another object of this invention to provide drill means adapted to be selectively lowered in a fishing string, engaging a positive rotational driving means in the fishing string and capable of simultaneously washing and rotationally drilling out rock or other debris from an object stuck in a well bore.

A further object of the invention is to provide drill means adapted to be selectively lowered within a fishing string containing a sub which provides a positive rotational driving connection between the fishing string and the drill apparatus. Alignment means facilitate formation of the driving connection as the drill means is lowered through the sub. Pressure means provide a downward force to the drill means while positive rotation of the fishing string and drill apparatus is accomplished. The drill means is selectively removable following cleanout operations.

It is still another object of this invention to facilitate the retrieval of drill pipe, drilling tools, or other equip ment stuck in a well bore and plugged with rock or other debris.

There is provided in accordance with this invention an improved method for retrieving a stuck object, the bore of which is plugged with rock or the like, from a well bore hole. To accomplish the method, a fishing string is provided with a sub adapted to transmit a positive rotational driving force to a selectively insertable drill means. The lower portion of the fishing string includes a sub which is adapted to engage the fish. Other usual devices for fishing operations may be present in the fishing string as desired. It the upper bore of the fish is plugged so that the engaging sub cannot immediately engage the fish, then the drill means is inserted into and lowered within the fishing string. As the drill means passes through the driving sub, a positive rotational driving connection is formed between the drill means and the fishing string. The drill means may then be rotated by the fishing string to drill out the plugging material until engagement of the fishing string with the fish can be effected. Forces are then applied to the fish to raise it from the well bore.

There is further provided in accordance with this invention an improved method for retrieving a stuck object, the bore of which is plugged with rock or the like, from a well bore. In carrying out this method a fishing string contains a sub adapted to transmit a positive rotational driving force to a selectively insertable drill means. A sub is adapted to engage the fish, and other usual devices for fishing operations are used. When the fishing string is lowered and engages the fish but is unable to dislodge the entire fish, disengagement of the freed portion of the fish is accomplished by a technique including the exploding of a charge within the joint to be released. A plugged bore in the freed portion of the fish prevents the lowering therethrough, to the proper location, of the explosive charge. This condition is ascertained, whereupon the drill means is lowered within the fishing string, forms a positive rotational driving connection with the fishing string, and is rotated by the fishing string to drill out the plugging material. The explosive charge is then lowered through the bore of the fishing string to the correct position within the fish, and retrieval operations are completed in the usual manner.

BRIEF DESCRIPTION OF THE DRAWINGS The manner in which the above objects and advantages of the invention, as well as others which will become apparent, are attained is explained more particularly in the following specification describing the present invention with reference to the drawings wherein:

FIGS. 1A and 1B are longitudinal partial sectional views illustrating a plugged pipe or fish within a well bore and showing a fishing string in accordance with this invention being lowered into position for operation to retrieve the stuck fish;

FIG. 2 is a cross-sectional top view of the fishing string at the location indicated by line 2-2 in FIG. 1, showing the detail of the positive rotational drive engagement between the driving sub and drill means passing through the sub;

FIG. 3 is a perspective view of the drive engagement means of the fishing string, and illustrating the alignment means located thereon; and

FIG. 4 is a longitudinal partial sectional view illustrating apparatus in accordance with this invention after engagement of the fishing string with a fish, the bore of which remains plugged.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in FIG. 1B, fish F is stuck in well bore 10. l n this illustration, the fish consists of drill pipe 12, drill pipe II, and any objects or equipment which may be connected below drill pipe 11. The sides of well bore have fallen in around the fish, as indicated by reference numeral 9. The formation which may have fallen in around drill pipe 12 has been washed away by usual retrieving apparatus and methods. Rock 14 has become lodged in the box of drill pipe 12,. preventing the connection of engaging pin 18 of connecting sub 16 with the box of the fish.

In accordance with the embodiment illustrated in FIGS. IA and 1B, a fishing string S is in a bore hole above a stuck piece of equipment, or fish, F. The lower end of fishing string S is provided with a connecting sub 16, a slip spline joint 20, and a driving sub 40. A central opening extends through the fishing string.

The lowermost portion of connecting sub 16 is provided with a pin connection 18 suitably sized to engage the open box connection of the fish. Of course, other commonly used connections may be provided on the connecting sub, depending on the connection of the fish, if any.

A selective rotation means, such as, for example, slip spline joint 20, is commonly used in fishing strings to permit the relative rotation of that portion of the string above the joint with respect to the rest of the string, and its use will be discussed below.

Driving sub 40 defines an annular, upwardly facing seat 42. Insert 44 is held in place within sub 40 by conventional means, such as shrink fitting or keying, and supported by seat 42. lnsert 44 defines a hexagonal bore adapted to rotationally drive a mating member passing through that bore. It will be apparent that any substantially noncircular seat, as well as other and different means, may be used in place of hexagonal insert 44 in sub 40 to enable the creation of a rotational driving connection between the fishing string and a member passing therethrough. Seat 44 also defines an upper surface 28 which is the first portion of an alignment means, the operation of which will be discussed below. In addition, fishing string S may contain other devices and subs customarily used, such as safety joints and the like, as deemed desirable and appropriate by the fishing string operator.

Drill pig 24 is shown in the bore 27 of the fishing string and has a central bore 22 communicating with the bore of the fishing string. Drill pig 24 has at its lower end a drill head or bit 30, containing mill teeth 32, and defining the lower end of bore 22. It will be appreciated that other suitable rock bits may readily be selected from bits well known to those skilled in the art and used in place of that illustrated in the present embodiment.

The central portion 25 of drill pig 24 is hexagonal and mates with the bore of insert 44. The lower end of the hexagonal portion 25 defines the second portion 26 of an alignment means which, in cooperation with the first portion 28 on insert 44 operates to rotate the drill pig until the hexagonal surface of the pig is aligned with the hexagonal bore of the insert. When the hexagonal portion of the pig is within the mating bore of insert 44, the pig will be rotationally driven by rotation of the fishing string.

FIGS. 2 and 3 illustrate in greater detail the relationship between insert 44 in driving sub 40 and the hexagonal cross section 25 of drill pig 24 when the mating hexagonal surfaces are adjacent, as well as the configuration of insert 44 particularly with respect to alignment means 28 at the upper end of the hexagonal in- 8811.

The central, hexagonal portion 25 of drill pig 24 may extend over a length sufficient to permit the rotational driving engagement between the pig and the driving sub to be effected when the fish is plugged at any point between its upper and lower ends. As the standard length for a section or joint of well pipe is 40 feet, the length of hexagonal portion 25 of the drill pig may be as much as forty or fifty feet or more, although shorter lengths may be quite satisfactory in many applications as will be understood by those skilled in the art.

Above the hexagonal portion of the drill pig are stop means to prevent the drill pig from passing completely through the bore of the fishing string. In FIG. 1A, annular element 36 is located at the lower end of swab cup 34, and element 36 will sit on upwardly facing shoulder 38 of the fishing string to retain the drill pig within the fishing string. Alternatively, stop means such as element 36 could act against insert 44, but the possibility of damage to the insert as a result of impacts between the annular element and the upper surface of the insert weigh against reliance on this alternative. Upwardly facing shoulder 38 will most conveniently be located closely above insert 44 in the fishing string to minimize the length of the drill pig between the driving engagement and the stop means, although any suitable location for shoulder 38 may be selected as will be apparent to those skilled in the art.

The upper portion 37 of drill pig 24 includes swab cup 34 which maintains a flexible seal between the exterior of the drill pig and the bore of the fishing string to minimize the flow of drilling fluid downwardly between the drill pig and the fishing string. Swab cup 34 is also useful in centering the drill pig within the fishing string, although other centering devices known in the art may be used. When a long drill pig is used, one or more additional swab cups or other centering means may be used to facilitate centering. However, the principal function of the swab cup is to permit the application of downward pressure on the drill pig by pumping drilling fluid down the fishing string, as will be further described below. At the uppermost end of the drill pig there is provided means 23 for attachment of a wire line or other retrieval device, so that the drill pig may be selectively withdrawn from the well bore as desired without the necessity for pulling the entire fishing string. This is particularly important in those applications involving a substantial amount of drilling, as drill head 30 may readily be replaced without having to pull the entire fishing string from the well bore.

lN OPERATION When an obstruction such as rock 14 is determined to be preventing the normal engagement of the fishing string with the fish, drill pig 24 is lowered downwardly through the fishing string. Although the drill pig will usually be lowered on a wire line, other known methods may be used, such as pumping the pig down the fishing string with drilling fluid. The drill pig is aligned with the hexagonal insert in sub 40 by alignment surfaces 26 and 28 which causes the drill pig to rotate until its hexagonal drive surface 25 is aligned with and passes through insert 44. When the drill pig's hexagonal portion is within insert 44, a driving connection is formed between the drill pig and the fishing string. The drill pig is lowered until its drill bit rests on obstructing rock 14. A rotational driving connection having been effected, rotation of the fishing string causes drill head 30 to rotate and drill away the obstruction.

Downward pressure may be maintained on the drill pig without positive latching of the drill pig to the fishing string by pumping drilling fluid downwardly through the bore of the fishing string, through the bore 22 of the drill pig communicating therewith, out the bottom of the drill head, and back up to the surface in the annulus between the fishing string and the well bore. As a pressure drop occurs in the drilling fluid as it flows through the bore of the drill pig, and as the upper surface of the drill pig and swab cup exposed to the fluid pressure is of greater cross section than the lower surface of the drill pig, a force differential is created across the drill pig by the flow of drilling fluid. This force acts downwardly upon the drill pig, assisting in the drilling out of rock 14 and improving the effectiveness ofthe drilling over that obtained when the only downward force utilized is the weight of the drill pig itself. The flow of drilling fluid in this manner further aids the retrieval process in that it assists in the washing out of any loose obstructing material as well as in washing away the debris which has been drilled out, as in any conventional drilling operation. Once the obstacle plugging the upper end of the fish has been removed, engaging pin 18 of connecting sub 16 may be connected to the fish and usual fishing operations undertaken to retrieve the fish.

F IG. 4 illustrates conditions in which another feature of this invention comes into play. If, after connecting sub 16 of the fish-ing string has engaged the upper end 12 of the fish, the entire fish cannot be removed by the fishing string because, for example, the formation has fallen in around the fish at a lower point, such as indicated by reference numeral 9, it is then usual in retrieval operations to disengage and remove the uppermost section, or sections, of the fish above the point at which the collapsed formation still holds the fish.

A common way of accomplishing disengagement of a free portion of a fish involves the lowering of an explosive charge within the bore of the fishing string to a point opposite the joint to be disengaged, as designated by reference numeral 13 in FIG. 4. As illustrated, however, debris 15 blocks the bore of drill pipe 12 such that the explosive charge cannot be lowered to the proper point for effecting disengagement of joint 13. In this situation, drill pig 24 may be lowered through the bore of the fishing string, forming a rotational driving connection with the driving sub. The driving sub is located above a selective rotation means, such as slip spline joint 20, in the fishing string, so that the fishing string can continue to rotate and drive the drill pig after connecting sub 16 has been firmly engaged with a nonrotatable fish. Subs defining selective rotation means are well known in the art and are used to prevent the fishing string from becoming stuck in the well bore during retrieval operations by permitting the continued rotation of a fishing string following engagement of the connecting sub with a non-rotatable fish. This capability to continue rotating the fishing string, and thereby to drive the drill pig, after the connecting sub has engaged the fish pennits the continued use of the drill pig to remove rocks and other debris plugging the fish below its uppermost end.

After debris 15 has been drilled out, the drill pig may be removed from the bore of the fishing string to allow positioning of an explosive charge adjacent joint 13. Because drill pig 24, as illustrated, has a central bore, it may be possible to lower the explosive charge through the drill pig so that removal of the upper section of the fish may be effected without having to pull the drill pig from the fishing string. When this procedure is followed, the drill pig is removed from the well bore with the fishing string and the disengaged section or sections of the fish. It will be appreciated that if the drill pig has been lowered into the fishing string by pumping rather than by lowering on a wire line, the explosive charge must necessarily be lowered through the bore of the drill pig unless the drill pig has been withdrawn with a wire line.

While the above description has referred to a preferred embodiment of the invention, it will be understood by those skilled in the art that various changes may be made in the construction of the apparatus and in the method of its use without departing from the spirit and scope of this invention, such as changing the size or shape of the drill head or the length of the drill pig, or by using the apparatus of this invention to wash debris from a stuck object prior to determining the need for undertaking the actual drilling step of the method disclosed above.

What is claimed is:

1. ln apparatus for retrieving equipment stuck in a well bore and including:

a fishing string adapted to be lowered within the well bore and having a central bore therethrough; and

engaging means at the lower end of the fishing string for engaging the stuck equipment; the improvement comprising:

drill means adapted to be selectively lowered through the bore of the fishing string and having:

a central bore therethrough communicating with the bore of the fishing string; and

a drill bit at the lower end of the drill means for drilling out material plugging the bore of the stuck equipment; and

drive means comprising a passage of substantially noncircular internal cross section within the bore of the fishing string, said passage being adapted to receive a mating region of substantially similar exterior cross section extending over a portion of the length of the drill means to prevent relative rotational motion between the fishing string and the drill means.

2. Apparatus as recited in claim 1 wherein the mating noncircular elements are substantially hexagonal in cross-sectional configuration.

3. ln apparatus for retrieving equipment stuck in a well bore and including:

a fishing string adapted to be lowered within the well bore and having a central bore therethrough; and

engaging means at the lower end of the fishing string for engaging the stuck equipment; the improvement comprising:

drill means adapted to be selectively lowered through the bore of the fishing string and having: a central bore therethrough communicating with the bore of the fishing string; and a drill bit at the lower end of the drill means for drilling out material plugging the bore of the stuck equipment; drive means disposed near the lower end of the fishing string for forming a positive rotational driving connection between the drill means and the fishing string when the drill means is engaged with the drive means; and

selective rotation means incorporated in the fishing string at a location below the drive means for permitting the selective relative rotation of that portion of the fishing string above said selective rotation means with respect to that portion of the fishing string below said selective rotation means. 4. Apparatus as recited in claim 3 wherein said selective rotation means is a slip spline joint.

5. ln apparatus for retrieving equipment stuck in a well bore and including: 7

a fishing string adapted to be lowered within the well bore and having a central bore therethrough; and

engaging means at the lower end of the fishing string for engaging the stuck equipment;

the improvement comprising:

drill means adapted to be selectively lowered through the bore of the fishing string and having:

a central bore therethrough communicating with the bore of the fishing string; and

a drill bit at the lower end of the drill means for drilling out material plugging the bore of the stuck equipment;

drive means disposed near the lower end of the fishing string for forming a positive rotational driving connection between the drill means and the fishing string when the drill means is engaged with the drive means; and

seal means disposed between the exterior of the drill means and the interior of the fishing string to permit application of a downward fluid pressure on the drill means.

6. Apparatus as recited in claim 5 wherein said seal means comprises a resilient wiper disposed around said drill means and adapted to provide a seal between said drill means and the interior of said fishing string.

7. ln apparatus for retrieving equipment stuck in a well bore and including:

a fishing string adapted to be lowered within a well bore and having a central bore therethrough;

engaging means at the lower end of the fishing string for engaging the stuck equipment; and

selective rotation means disposed near the lower end of the fishing string for permitting the rotation of that part of the fishing string above said selective rotation means independent of that part of the fishing string below said selective rotation means;

the improvement comprising:

drill means adapted to be selectively lowered through and removed from the bore of the fishing string and having:

a central bore extending entirely therethrough and communicating with the bore of the fishing string;

a drill bit at the lower end of the drill means and ex tending below the lowermost surface of the fishing string for drilling out material plugging the bore of the stuck equipment;

means forming a positive rotational driving connection between the drill means and a corresponding drive means disposed above the selective rotation means in the fishing string; and

means producing a downward force on the drill means responsive to flow of drilling fluid therethrough.

8. In apparatus for retrieving equipment stuck in a well bore and including:

a fishing string adapted to be lowered within a well bore and having a central bore therethrough; and

engaging means at the lower end of the fishing string for engaging the stuck equipment;

the improvement comprising:

a drive sub adapted to be disposed near the lower end of the fishing string and having a central bore therethrough communicating with the bore of the fishing string;

means defining a noncircular passage within the bore of the drive sub;

drill means adapted to be selectively lowered through and removed from the fishing string and having:

a central bore therethrough communicating with the bore of the fishing string;

a drill bit at the lower end of the drill means and extending below the lowermost surface of the fishing string;

an upper section of substantially the same external diameter as the diameter of the bore of the fishing string above the drive sub, the lower end of said upper section being adapted to sit on an upwardly facing shoulder in the fishing string to prevent passage of the drill means through the fishing string; and

a lower section having a noncircular exterior cross section of mating configuration with the noncircular passage in the drive sub for forming an engagement therewith, whereby rotation of the fishing string will rotate the drill means.

9. Apparatus as recited in claim 8 wherein the lowermost portion of said lower section comprises a pilot section to orient said drill means in said noncircular passage.

10. Apparatus as recited in claim 8 wherein aligning means are provided for bringing the noncircular elements into alignment as the drill means is lowered through the noncircular passage defined within the drive sub.

11. Apparatus as recited in claim 10 wherein said aligning means comprises cooperating inclined surfaces on said drill means and said drive sub adapted to align said lower section with said noncircular passage.

12. The method of retrieving stuck equipment having a plugged bore from a well bore, including the steps of:

lowering into the well bore a fishing string having engaging means at the lower end thereof for engaging the stuck equipment;

lowering drill means, having a drill bit at its lower end, downwardly through the fishing string to a position where the drill bit rests on the material plugging the bore of the stuck equipment;

forming a positive rotational driving connection between said drill means and the fishing string;

rotating the drill means to drill out the material plugging the bore of the stuck equipment;

engaging the stuck equipment with the engaging means at the lower end of the fishing string; and

manipulating the fishing string after the stuck equip ment has been engaged to exert forces on the stuck equipment.

13. The method as recited in claim 12 including the step of maintaining downward fluid pressure on said drill means during rotation thereof.

14. The method as recited in claim 12 including the step of providing a flow of drilling fluid to said drill means during the drilling out of the plugging material to wash debris from the stuck equipment.

15. The method as recited in claim 12 including, after engaging the stuck equipment with the fishing string, the further steps of:

drilling out material plugging the bore of the fish to a free joint thereof;

lowering an explosive charge downwardly through the fishing string to a position adjacent said free joint of the stuck equipment and exploding the charge; and

pulling the fishing string with the unstuck equipment engaged therewith out of the well bore.

16. The method as recited in claim 15 wherein the explosive charge is lowered through the drill means into position within the stuck equipment.

17. Apparatus for use in retrieving equipment stuck in a well bore, comprising:

drill means adapted to be selectively lowered through and removed from the bore of a fishing string, said drill means having:

a central bore therethrough communicating with the bore of the fishing string;

a drill bit at the lower end of the drill means for drilling out material from the bore of the stuck equipment;

an upper section including means adapted to sit on an upwardly facing shoulder in the fishing string to prevent passage of the drill means through the fishing string;

a lower section including a noncircular exterior cross section adapted to mate with a corresponding noncircular passage in the fishing string to form a positive rotational driving connection therewith; and

means for producing a downward force on the drill means when drilling fluid is flowed through the bore thereof.

18. Apparatus as recited in claim 17, wherein said means for producing a downward force on the drill means comprises a seal disposed about the exterior of the drill means and adapted to seal against the interior of the fishing string when the drill means is within the bore of the fishing string, whereby flow of drilling fluid downwardly within the bore of the fishing string will produce said downward force.

I I i I! I. 

1. In apparatus for retrieving equipment stuck in a well bore and including: a fishing string adapted to be lowered within the well bore and having a central bore therethrough; and engaging means at the lower end of the fishing string for engaging the stuck equipment; the improvement comprising: drill means adapted to be selectively lowered through the bore of the fishing string and having: a central bore therethrough communicating with the bore of the fishing string; and a drill bit at the lower end of the drill means for drilling out material plugging the bore of the stuck equipment; and drive means comprising a passage of substantially noncircular internal cross section within the bore of the fishing string, said passage being adapted to receive a mating region of substantially similar exterior cross section extending over a portion of the length of the drill means to prevent relative rotational motion between the fishing string and the drill means.
 2. Apparatus as recited in claim 1 wherein the mating noncircular elements are suBstantially hexagonal in cross-sectional configuration.
 3. In apparatus for retrieving equipment stuck in a well bore and including: a fishing string adapted to be lowered within the well bore and having a central bore therethrough; and engaging means at the lower end of the fishing string for engaging the stuck equipment; the improvement comprising: drill means adapted to be selectively lowered through the bore of the fishing string and having: a central bore therethrough communicating with the bore of the fishing string; and a drill bit at the lower end of the drill means for drilling out material plugging the bore of the stuck equipment; drive means disposed near the lower end of the fishing string for forming a positive rotational driving connection between the drill means and the fishing string when the drill means is engaged with the drive means; and selective rotation means incorporated in the fishing string at a location below the drive means for permitting the selective relative rotation of that portion of the fishing string above said selective rotation means with respect to that portion of the fishing string below said selective rotation means.
 4. Apparatus as recited in claim 3 wherein said selective rotation means is a slip spline joint.
 5. In apparatus for retrieving equipment stuck in a well bore and including: a fishing string adapted to be lowered within the well bore and having a central bore therethrough; and engaging means at the lower end of the fishing string for engaging the stuck equipment; the improvement comprising: drill means adapted to be selectively lowered through the bore of the fishing string and having: a central bore therethrough communicating with the bore of the fishing string; and a drill bit at the lower end of the drill means for drilling out material plugging the bore of the stuck equipment; drive means disposed near the lower end of the fishing string for forming a positive rotational driving connection between the drill means and the fishing string when the drill means is engaged with the drive means; and seal means disposed between the exterior of the drill means and the interior of the fishing string to permit application of a downward fluid pressure on the drill means.
 6. Apparatus as recited in claim 5 wherein said seal means comprises a resilient wiper disposed around said drill means and adapted to provide a seal between said drill means and the interior of said fishing string.
 7. In apparatus for retrieving equipment stuck in a well bore and including: a fishing string adapted to be lowered within a well bore and having a central bore therethrough; engaging means at the lower end of the fishing string for engaging the stuck equipment; and selective rotation means disposed near the lower end of the fishing string for permitting the rotation of that part of the fishing string above said selective rotation means independent of that part of the fishing string below said selective rotation means; the improvement comprising: drill means adapted to be selectively lowered through and removed from the bore of the fishing string and having: a central bore extending entirely therethrough and communicating with the bore of the fishing string; a drill bit at the lower end of the drill means and extending below the lowermost surface of the fishing string for drilling out material plugging the bore of the stuck equipment; means forming a positive rotational driving connection between the drill means and a corresponding drive means disposed above the selective rotation means in the fishing string; and means producing a downward force on the drill means responsive to flow of drilling fluid therethrough.
 8. In apparatus for retrieving equipment stuck in a well bore and including: a fishing string adapted to be lowered within a well bore and having a central bore therethrough; aNd engaging means at the lower end of the fishing string for engaging the stuck equipment; the improvement comprising: a drive sub adapted to be disposed near the lower end of the fishing string and having a central bore therethrough communicating with the bore of the fishing string; means defining a noncircular passage within the bore of the drive sub; drill means adapted to be selectively lowered through and removed from the fishing string and having: a central bore therethrough communicating with the bore of the fishing string; a drill bit at the lower end of the drill means and extending below the lowermost surface of the fishing string; an upper section of substantially the same external diameter as the diameter of the bore of the fishing string above the drive sub, the lower end of said upper section being adapted to sit on an upwardly facing shoulder in the fishing string to prevent passage of the drill means through the fishing string; and a lower section having a noncircular exterior cross section of mating configuration with the non-circular passage in the drive sub for forming an engagement therewith, whereby rotation of the fishing string will rotate the drill means.
 9. Apparatus as recited in claim 8 wherein the lowermost portion of said lower section comprises a pilot section to orient said drill means in said noncircular passage.
 10. Apparatus as recited in claim 8 wherein aligning means are provided for bringing the noncircular elements into alignment as the drill means is lowered through the noncircular passage defined within the drive sub.
 11. Apparatus as recited in claim 10 wherein said aligning means comprises cooperating inclined surfaces on said drill means and said drive sub adapted to align said lower section with said noncircular passage.
 12. The method of retrieving stuck equipment having a plugged bore from a well bore, including the steps of: lowering into the well bore a fishing string having engaging means at the lower end thereof for engaging the stuck equipment; lowering drill means, having a drill bit at its lower end, downwardly through the fishing string to a position where the drill bit rests on the material plugging the bore of the stuck equipment; forming a positive rotational driving connection between said drill means and the fishing string; rotating the drill means to drill out the material plugging the bore of the stuck equipment; engaging the stuck equipment with the engaging means at the lower end of the fishing string; and manipulating the fishing string after the stuck equipment has been engaged to exert forces on the stuck equipment.
 13. The method as recited in claim 12 including the step of maintaining downward fluid pressure on said drill means during rotation thereof.
 14. The method as recited in claim 12 including the step of providing a flow of drilling fluid to said drill means during the drilling out of the plugging material to wash debris from the stuck equipment.
 15. The method as recited in claim 12 including, after engaging the stuck equipment with the fishing string, the further steps of: drilling out material plugging the bore of the fish to a free joint thereof; lowering an explosive charge downwardly through the fishing string to a position adjacent said free joint of the stuck equipment and exploding the charge; and pulling the fishing string with the unstuck equipment engaged therewith out of the well bore.
 16. The method as recited in claim 15 wherein the explosive charge is lowered through the drill means into position within the stuck equipment.
 17. Apparatus for use in retrieving equipment stuck in a well bore, comprising: drill means adapted to be selectively lowered through and removed from the bore of a fishing string, said drill means having: a central bore therethrough communicating with the bore of the fishing string; a drill bit at the lower end of The drill means for drilling out material from the bore of the stuck equipment; an upper section including means adapted to sit on an upwardly facing shoulder in the fishing string to prevent passage of the drill means through the fishing string; a lower section including a noncircular exterior cross section adapted to mate with a corresponding noncircular passage in the fishing string to form a positive rotational driving connection therewith; and means for producing a downward force on the drill means when drilling fluid is flowed through the bore thereof.
 18. Apparatus as recited in claim 17, wherein said means for producing a downward force on the drill means comprises a seal disposed about the exterior of the drill means and adapted to seal against the interior of the fishing string when the drill means is within the bore of the fishing string, whereby flow of drilling fluid downwardly within the bore of the fishing string will produce said downward force. 